The present invention relates to the use of pneumatic ducting systems in aircraft structures. Amongst the prior art, it is well known to use high temperature, high pressure bleed air from the engines for various on-board purposes in a modern aircraft. It is also well known to use high temperature, high pressure gases to start aircraft engines.
Bleed air, or the high pressure hot air drawn from the aircraft engine's compressor stages, is routed through an aircraft to serve multiple purposes, including starting additional engines, pressurizing the cabin, de-icing the wings, nacelles, and empennage, and supporting the aircraft's air conditioning units, along with various other systems. The bleed air must therefore be transported from the engines to various other areas of the aircraft, using appropriate ducting systems, capable of withstanding high pressures, high temperatures, as well as the stresses of vibration, impact, acceleration, deceleration, aircraft component deflection and momentum. FIG. 1 depicts a high-level block diagram of a pneumatic ducting system for an aircraft, including the various potential components of the system, and the ducts that connect the components, for routing bleed air and other pressurized gases within the system. Such ducting systems typically utilize insulated metallic duct sections ranging in diameter from 1.00″ to 6.50″ and ranging in length from at least 6″. The air in the duct can reach pressures up to 450 psig and reach temperatures of up to 1200° F., but is typically at a pressure of 60 psig and 800° F. in temperature.
The ducting systems are designed to expand and contract under thermal loading due to the flow of high temperature air. The ducting systems comprise numerous branches and junctions, to route the bleed air from the engines to the various systems and locations mentioned above. To account for thermal expansion, tolerances, and interface displacements due to the above-identified forces, a tension duct system (one where fluid column or longitudinal forces resulting from internal pressure are not transferred to the surrounding airplane structures, as defined in SAE ARP 699, ¶ 4.2.1) typically contains flexible joints that provide motion compensation. Such flexible joints are often used to connect two duct sections together, and are designed to relieve stresses and compensate for bending loads. SAE ARP 699 ¶ 5.1.2 defines the typical flex joint designs commonly used in modern aircraft.
The term “joint” is used herein to refer to a flexible motion compensator between two (and only two) duct sections, thereby enabling the pressurized gases within one duct portion to travel through the joint and into the next duct portion, wherein the two duct portions collectively form a single elongated duct section (containing a joint therewithin). In addition to such joints, aircraft ducting systems typically include one or more intersection points where a single duct portion can branch off into two or more duct portions, so that gases from the first duct portion can flow into multiple duct portions in different directions, to multiple locations throughout the aircraft. In the past, such intersection points have often comprised a three-way (or more) “junction,” in which each of the duct sections may be connected to the junction via a standard, conventional flexible duct joint. Such standard duct joints enable movement between one duct portion and the junction—to accommodate rotation or translation due to thermal expansion, as well as all stresses or displacements that may arise from such highly pressurized, hot gases occurring in an accelerating or decelerating aircraft, complete with vibration, impacts and aircraft component deflection. Accordingly, the term “junction” is used herein to refer to a connection interface between three or more duct sections, thereby enabling the pressurized gases within one duct portion to travel through the junction and into multiple other duct portions, each of which carries the gases in a different direction.
A typical three-way junction is in the shape of a “Y” and serves to connect three separate duct portions together, each by way of a standard, conventional flexible duct joint. Such a conventional three-way “Y” junction is shown in FIG. 2 of the present application. Notably, junctions for separating or condensing high temperature, pressurized gases must be capable of withstanding the high temperatures and pressures thereof, amongst other stresses. For this reason, conventional junctions like junction 10 are typically made from thicker materials, which cause those junctions to weigh and cost more. Moreover, the junctions inherently require the use of duct joint assemblies at or near the branches of the junctions, which likewise adds considerable weight and costs. In addition, for tension system designs, such duct joint assemblies only provide transverse/bending angulation freedom at each branch leg (i.e., 2 rotational degrees of freedom)—and the bending moment due to friction in the joints does not relieve all of the loads on the junction, thereby causing considerable stresses to still occur. As a result, aircraft ducting systems containing prior art duct junctions are typically designed with high wall thickness to ensure positive stress margins for all applied conditions.
It is desirable to improve the design of duct system junctions by decreasing their overall weight and cost—not only by using thinner materials, but also by minimizing the number of ducting joint assemblies within the system, while still allowing for relative angular, rotational and translational movement between different branches at a duct junction—while eliminating or minimizing stress concentrations at conventional or welded duct junctions. It is also desirable to relieve stresses on the junctions with minimal leakage, while maintaining the tension in the system and preventing fluid forces from being transmitted to the supporting aircraft structures.